How to create a fake fire/flame?
For a shader only solution, one way is a simple material such as the following:

Click to enlarge
Blackbody Node is used for color.
See kelvin color temperature for some examples of values to start with. You can adjust these values up and down until you get something you like.
The layer weight node is used for a mixing factor between the two blackbody nodes creating a result like below:

An approach like this should keep resources low and be fairly manageable. Note that also, the flame object is a quad-sphere modeled to a flame and not a flat plane.